This invention relates to a blood filter cartridge for the preparation of a plasma or serum sample from whole blood.
The type or concentration of blood components, such as metabolites, proteins, lipids, electrolytes, enzymes, antigens, and antibodies, is measured, in general, using a plasma or serum sample obtained by centrifuging whole blood. However, centrifuging takes labor and time. Particularly, centrifuging is unsuitable for an urgent case of measuring a small number of samples promptly and in site inspection, because of requiring a centrifuge and electricity. Thereupon, it has been investigated to separate serum from whole blood by filtration.
Several filtration methods using glass fiber filter have been developed wherein whole blood is charged into the glass fiber put in a column from one side of the column, and pressurized or evacuated to obtain plasma or serum from the other side (Japanese Patent KOKOKU Nos. 44-14673, 5-52463, Japanese Patent KOKAI Nos. 2-208565, 4-208856).
However, practical filtration methods capable of obtaining an amount of plasma or serum from whole blood necessary for measuring by an automatic analyzer have not been developed except a part of items, such as blood sugar.
On the other hand, the inventors developed a blood filter cartridge composed of a filter holder and a syringe. The filter holder is composed of a holder body which contains filter material and a cap which is screwed on the holder body. The filter material consists of, e.g. two sheets of glass fiber filter, one sheet of cellulose filter and one sheet of polysulfone microporous membrane (FIG. 1 of EP 785430 A1)
Another blood filter cartridge composed of a holder body and a cap was also developed. The holder body consists of a plasma receiver located on the upper side and a filter chamber located on the underside. The filter material put in the filter chamber is composed of six sheets of glass fiber filter and one sheet of polysulfone microporous membrane (Example 1 of EP 785012A1).
The inventors further developed various blood filter cartridges, and their patent applications were made (Japanese Patent KOKAI 10-227788, 10-185909, 10-185780, etc.)
However, since the above blood filter cartridges are of a type of attaching a suction nozzle to the blood inlet and sucking blood from a blood collecting tube, a part of blood essentially remains in the blood collecting tube and the suction nozzle without filtered. As a result, the volume of drawn blood increases to add a burden to a person who takes a medical inspection. Particularly, in the case of clinical assay using a dry analytical element, although analysis of plural items can be achieved by using about 100 to 500 .mu.l plasma, the volume of drawn blood, in general, exceeds 10 ml.